Re: [PATCH v8 00/11] KVM: MMU: fast zap all shadow pages

From: Xiao Guangrong
Date: Sun Jun 09 2013 - 05:06:41 EST

On 06/09/2013 04:53 PM, Gleb Natapov wrote:
> On Fri, May 31, 2013 at 08:36:19AM +0800, Xiao Guangrong wrote:
>> Hi Gleb, Paolo, Marcelo,
>> I have putted the potential controversial patches to the latter that are
>> patch 8 ~ 10, patch 11 depends on patch 9. Other patches are fully reviewed,
>> I think its are ready for being merged. If not luck enough, further discussion
>> is needed, could you please apply that patches first? :)
>> Thank you in advance!
>> Some points are raised during discussion but missed in this version:
>> 1) Gleb's idea that skip obsolete pages in the hast list walker
>> Unfortunately, it is not safe. There has a window between updating
>> valid-gen and reloading mmu, in that window, the obsolete page can
>> be used by vcpu, but the guest page table fail to be write-protected
>> (since the obsolete page is skipped in mmu_need_write_protect()).
> Can you elaborate on how this can happen. valid_gen is updated under
> mmu_lock and reloading of mmus happens under the same lock, so for all
> other vcpus this should look like atomic thing.

You're right.

Actually, i made another optimization patch in this version that moves
kvm_reload_remote_mmus() out of mmu-lock, but did not attach it into this
series. It seems my brain is not parallel-able enough. :(

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